1. Field of the Invention
The present invention relates a belt device for use in an image forming apparatus.
2. Description of the Related Art
Tandem color image forming apparatuses, such as copiers and printers, including an intermediate transfer belt (belt device) are well-known in the art. Such image forming apparatuses have been disclosed in, for example, Japanese Patent Application Laid-open No. 2006-343629 and Japanese Patent No. 3473148.
In a typical image forming apparatus, four photosensitive drums (image carriers) are provided side by side facing an intermediate transfer belt (belt member). Single-color toner images for black, yellow, magenta, and cyan are respectively formed on each of the four photosensitive drums. Those single-color toner images are then transferred so as to be overlaid on top of each other on the intermediate transfer belt to form a color toner image on the intermediate transfer belt. The color toner image supported on the intermediate transfer belt is then transferred to and fixed on a recording medium, such as a paper, as a color image.
Technology where displacement of an intermediate transfer belt in a widthwise direction is detected and the displacement in a widthwise direction is corrected based on results of the detection is well-known. The object of such technology is to suppress falling of the image quality due to meandering of the intermediate transfer belt and to prevent the intermediate transfer belt from becoming damaged due to being substantially displaced in a widthwise direction and coming into contact with other members.
Various method are available for correcting displacement of the intermediate transfer belt in a widthwise direction. In one known method (hereinafter, “steering method”), an angle of inclination of the intermediate transfer belt from a reference surface is adjusted by adjusting an inclination of a roller that supports the intermediate transfer belt. Such a method has been disclosed in, for example, Japanese Patent Application Laid-open No. 2006-343629 and Japanese Patent No. 3473148. In another know method (hereinafter, “belt guide method”), the edges of the intermediate transfer belt are guide so as to suppress displacement of the intermediate transfer belt. The steering method is advantageous compared to the belt guide method in that the load placed on the intermediate transfer belt is much smaller which increases the durability of the intermediate transfer belt.
Specifically, in Japanese Patent Application Laid-open No. 2006-343629, an extent of displacement of a contact that abuts with an end in a width direction of the intermediate transfer belt (endless belt) and reciprocates in accordance with displacement of the intermediate transfer belt is detected by a displacement sensor. Displacement (meandering) of the intermediate transfer belt is then corrected by a meandering correction roller based on the detection results of the displacement sensor.
On the other hand, technology also exists for correcting meandering by periodically detecting meandering of a belt member such as an intermediate transfer belt or a transport belt. Such technology is disclosed in Japanese Patent No. 3473148. This technology accurately detects meandering of the belt member while excluding meandering characteristics peculiar to the rollers and meandering characteristics peculiar to the belt. This is achieved by matching the timing of detecting meandering of the belt member with a rotational period of the roller member (roller) and belt period.
In order to accurately detect an amount of displacement in a widthwise direction of the belt member using a detecting unit without influencing cutting tolerance (a wave-like cutting mark occurring during cutting processing) for both ends of the belt member in a widthwise direction, the amount of displacement in a widthwise direction of the belt member is sampled periodically (at fixed time intervals) by a detecting unit. Meandering correction for the belt member is then performed based on the sampled data. However, when the speed of travel of the belt member accelerates or decelerates, the sampled data is not for equal intervals with respect to the direction of travel of the belt member. Therefore, the sampled data is affected by the cutting tolerance of the belt member so that it is no longer possible to accurately detect the amount of displacement in the widthwise direction of the belt member.
Linear process speed is fast and higher durability is required in high-speed image forming apparatuses. In particular, it is common with high-speed apparatus where the belt member travels at high-speed for acceleration (slow starting) to be carried out when the belt member starts to travel and for deceleration (slow down) to be carried out when traveling of the belt member ends. This is in order to suppress abrupt loads from being applied to configuration components constituting the belt device such as, for example, motors and gears. It is therefore not possible to ignore the problems explained above. Such problems are not limited to belt devices using an intermediate transfer belt as a belt member, but are common to even other belt devices that detect and correct displacement of belt members such as belt devices using a transfer belt as a belt member or belt devices using a photosensitive belt as a belt member.